Lithium-ion-conducting composite material and process for producing

ABSTRACT

A lithium-ion-conducting composite material and process of producing are provided. The composite material includes at least one polymer and lithium-ion-conducting particles. The particles have a sphericity Ψ of at least 0.7. The composite material includes at least 20 vol % of the particles for a polydispersity index PI of the particle size distribution of &lt;0.7 or are present in at least 30 vol % of the composite material for the polydispersity index in a range from 0.7 to &lt;1.2, or are present in at least 40 vol % of the composite material for the polydispersity index of &gt;1.2.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC § 119 of GermanApplication No. 102017128719.1 filed Dec. 4, 2017, the entire contentsof which are incorporated herein by reference.

BACKGROUND 1. Field of the Invention

The invention relates to a lithium-ion-conducting composite materialcomprising at least one polymer and lithium-ion-conducting particles andto a process for producing a lithium ion conductor from the compositematerial.

2. Description of Related Art

Over recent years, lithium-ion batteries and lithium batteries haveacquired ever greater importance, especially for electronic devices, butalso in the field of electric vehicles, for reasons in particular oftheir high energy densities, the absence of memory effects, and the veryslow rate at which they suffer voltage drop. Lithium-ion batteries andlithium batteries in general comprise a family of rechargeable batteries(also referred to as secondary batteries) which are used as powerstorage media for the fields identified above.

A lithium-ion battery or lithium battery consists fundamentally of threemain structural units, these being the anode (negative electrode), thecathode (positive electrode) and the non-aqueous electrolyte, which isdisposed between the two electrodes and which brings about the movementof the lithium ions in operation (charging or discharge). In the case ofthe lithium-ion batteries, the anode is customarily graphite-based, withlithium ions being intercalated into this anode during charging andgiven up from this anode on discharge. In the case of the lithiumbatteries, conversely, the anode used comprises elemental lithium.

At present, the lithium-ion batteries that are available commerciallyuse primarily electrolytes in which a lithium salt is in solution in anorganic solvent. A disadvantage of these lithium-ion batteries, however,is that in the case of misuse or under extreme loads, they mayself-destruct and, in the most extreme case, may catch fire when theydo.

In order to solve these problems, a particular focus of investigation inrecent years has been that of what are called solid-state lithiumbatteries, in which the liquid, organically based electrolyte matrix isreplaced by a solid, which is still lithium-conductive. In this case,very generally, the solid-state electrolyte in the battery system can beused at various locations: on the one hand, a conceivable use of thepure solid-state electrolyte is as a separator—introduced between theelectrodes, it preserves them from unwanted short-circuiting and sosecures the functional capacity of the system as a whole. For thispurpose, the solid-state electrolyte may either be applied as a layer toone or both electrodes, or integrated as a free-standing membrane intothe battery. Also conceivable is for the solid-state electrode to becompounded with the active electrode materials. In that case, theelectrolyte brings about the transport of the relevant charge carries(lithium ions and electrons) to the electrode materials and to or awayfrom the conducting electrodes, according to whether the battery isbeing discharged or charged.

In principle, solid-state electrolytes may comprise a polymerelectrolyte or a polyelectrolyte. In the case of the former—similarly tothe liquid electrolytes—a lithium-based conductive salt is in solutionin a solid polymer matrix (for which purpose polyethylene oxide isfrequently employed). In the second case, the systems in question arepolyfunctional lithium salts of a polymer. Both electrolytes—polymerelectrolytes and polyelectrolytes—are similar to the liquid-basedelectrolytes in having, in general, insufficient chemical andelectrochemical stability with respect to elemental lithium, and aretherefore less suitable for use in lithium batteries. Alternatively,however, it is also possible to conceive of using a purely inorganicsolid-state ion conductor as replacement for the organically basedliquid electrolytes that have been used to date. Particularly promisingin this context with regard to their lithium-ion conductivity areoxide-based (e.g. lithium-conducting mixed oxides with garnet-likestructure), phosphate-based and sulfide-based materials that conductlithium ions. Certain variants of these have sufficient chemical andelectrochemical stability with respect to elemental lithium. They aretherefore suitable for use in lithium batteries. For otherrepresentatives of the class of the purely inorganic solid-state ionconductors, however, this is not the case. The possibility of deployingsuch a material as a solid-state electrolyte in lithium batteries musttherefore be examined separately again in each individual case. A thirdvariant of a lithium-conducting solid is represented by what are calledthe hybrid electrolytes: these comprise a composite material whereinparticles of an inorganic, lithium-ion-conducting material areincorporated into a lithium-conducting polymer matrix consisting of apolymer electrolyte or polyelectrolyte. Certain hybrid electrolytevariants likewise display sufficient chemical and electrochemicalstability with respect to elemental lithium and so likewise possess thepotential for use in lithium batteries.

Among the purely inorganic solid electrolytes that conduct lithium ions,the sulfidic compositions Li—S—P and Li₂S—P₂S₅—P₂O₅ are sometimesprepared by grinding of the reactants under inert gas and by subsequenttemperature treatment (generally likewise under inert gas). Theproduction of Li—P—S glass-ceramics is described in the texts US20050107239 A1, US 2009159839 A and JP 2008120666 A. Li₂S—P₂S₅—P₂O₅ maybe prepared—as by A. Hayashi et al., Journal of non-Crystalline Solids355 (2009) 1919-1923—either via a grinding operation or else via themelt. Glass-ceramics composed of the system Li₂S—B₂S₃—Li₄SiO₄ as wellmay be produced via the melting route with subsequent quenching,although these operations as well should be conducted in the absence ofair (see US 2009011339 A and Y. Seino et al., Solid State Ionics 177(2006) 2601-2603). The attainable lithium-ion conductivities are from2×10⁻⁴ to 6×10⁻³ S/cm at room temperature. To be borne in mind in thecase of the sulfidic solid electrolytes that conduct lithium ions is thefact that production under inert gas and the sometimes complicatedgrinding operations may make them more expensive to produce. Handlingand storage as well, moreover, frequently have to be done under inertgas, or at least in a water-free environment, something which undercertain circumstances may be a disadvantage for the production of thelithium batteries.

Conversely, the solid-state lithium-ion conductors that are based onoxidic systems feature simpler and hence more favourable production andgreater chemical stability. Known representatives include primarilyphosphate-based compositions with crystal phases which have a crystalstructure similar to NASICON (sodium super-ionic conductor). Customarilythese are glass-ceramics, in which case first of all a starting glass ismelted and subjected to hot shaping (e.g. casting). The starting glass,in a second step, is ceramicized either directly (“bulk glass-ceramic”)or as a powder (“sintered glass-ceramic”). Ceramicization, through anappropriately selected temperature-time regime, may involve a controlledcrystallization, permitting the establishment of a glass-ceramicstructure optimized for lithium-ion conductivity. As a result it ispossible to achieve an improvement in the conductivity of the order ofmagnitude of more than one factor of ten. The text US 20030205467 A1describes the production of glass-ceramics from P₂O₅, TiO₂, SiO₂, M₂O₃(M=Al or Ga) and Li₂O, with the main crystal phase Li_((1+x))(Al,Ga)_(x)Ti_((2−x))(PO₄)₃ (0<x≤0.8). After crystallization, an ionconductivity of 0.6 to 1.5×10⁻³ S/cm was achieved. The starting glassesare very susceptible to crystallization and must be quenched on a metalplate in order to prevent uncontrolled crystallization. This limits thepossibilities for shaping and for establishment of structure in theglass-ceramic.

In the texts U.S. Pat. Nos. 6,030,909 and 6,485,622, GeO₂ and ZrO₂ areadditionally introduced into the glass-ceramic. GeO₂ enlarges theglass-forming range and reduces the crystallization tendency. Inpractice, however, this positive effect is limited by the high price ofthe germanium raw material. ZrO₂, in contrast, leads to anintensification of the crystallization. The starting glasses identifiedin these texts also tend towards uncontrolled crystallization and mustgenerally be quenched in order to give a suitable starting glass.

In Electrochem. Commun., 6 (2004) 1233-1237, and in Materials Letters,58 (2004), 3428-3431, Xu et al. describe Li₂O—Cr₂O₃—P₂O₅ glass-ceramicswhich likewise have high conductivities of 5.7×10⁻⁴ to 6.8×10⁻⁴ S/cm.These starting glasses as well, however, have to be quenched, owing to astrong tendency to crystallize.

There are also descriptions of glass-ceramics which contain Fe₂O₃(K.Nagamine et al., Solid State Ionics, 179 (2008) 508-515). Here, ionconductivities of 3×10⁻⁶ S/cm were found. However, the use of ion (orother polyvalent elements) frequently leads to the occurrence ofelectronic conductivity, which must be avoided in a solid-stateelectrolyte. In accordance with JP 2008047412 A, therefore, thisglass-ceramic is used preferably as a cathode material, where electronicconductivity is desirable in order to facilitate the contacting of thecathode.

US 2014/0057162 A1 describes lithium-ion-containing phosphate-basedglass-ceramics which exhibit an ion conductivity of at least 5×10⁻⁷ S/cmand feature starting glasses which have sufficient crystallizationstability, allowing them to be produced from the melt by casting withoutthe need for quenching. Both the glass-ceramics and the starting glassesalso have sufficient chemical stability in air, permitting storage. Thereason why this is possible is that the corresponding phosphate-basedglass-ceramics comprise Ta₂O₅ and/or Nb₂O₅. Ta₂O₅ and Nb₂O₅ improve thecrystallization stability of the glass and, owing to the fact that theycan likewise be incorporated into the crystal phase, have a positiveinfluence on the ion conductivity, by raising the crystal-phasefraction.

A class of substance which, among the oxide-based, inorganic,solid-state ion conductors, is of particular interest on account oftheir high lithium-ion conductivity is that of lithium-containing mixedoxides with a garnet-like structure, as described in the text DE102007030604 A1. Particularly high conductivity in this context ispossessed by the class of materials with zirconium and lanthanum that intheir simplest form have the formula Li₇La₃Zr₂O₁₂. The latter compoundor compounds derived from it is frequently also referred to for shortsimply as LLZO. This garnet occurs in two modifications, a tetragonaland a cubic modification. Since in particular the cubic modification ofLLZO has a high lithium-ion conductivity, the cubic modification of LLZOis of particular interest for solid-state lithium batteries. Furtherinvestigations on LLZO have shown that the formation of the cubicmodification of LLZO can be stabilized in particular with addition offurther metals for doping, such as aluminium, for example. For thepurposes of the present specification, lithium lanthanum zirconiumoxides, undoped or doped, or compounds derived therefrom, are referredto generally as LLZO. In the past, LLZOs have proven to be chemicallyand electrochemically stable with respect to the elemental lithiumemployed as anode in lithium batteries, and so possess a great potentialfor use as an electrolyte in corresponding systems.

The literature gives a number of methods for preparing LLZO. Forinstance, on the one hand, “solid-phase” processes are known for thepreparation of LLZO, as are described in US 2010/047696 A1 or in US2010/0203383 A1, for example. In the process described in the latterdocument, the starting materials, previously dried in some cases attemperatures up to 900° C., are ground for 12 hours in a ball mill, thenheated for 12 hours at temperatures between 900 and 1125° C.; theproduct obtained is then ground again in a ball mill. After that, theresulting powder is subjected to isostatic pressing and calcined againat temperatures in the region of 1230° C. for 36 hours. Alternatively tothe solid-phase processes, attempts have been made to prepareprecursors, using the sol-gel process which can then be processedfurther to form the desired crystalline mixed oxides with garnetstructure. One process of this kind, sometimes also described as thePechini process, is described in Y. Shimonishi et al, Solid State Ionics183 (2011) 48-53, for example. In this case, lithium, lanthanum andzirconium are used in the form of the nitrates and are heated togetherin a mixture of water, citric acid and ethylene glycol, to form a blacksolid, which must then be heat-treated at 350° C. for five hours, beforean intermediate in powder form is obtained which can then be processedfurther to the desired end product. DE 102013101145 A1 and DE102013224045 A1 describe the production of cubically or tetragonallycrystallizing LLZO via the sol-gel process, starting in one case from analcohol-based sol and in the other case from a water-based sol. US2011/0053001 A1 discloses a further sol-gel process for producingamorphous LLZO.

DE 102014116378 A1 discloses the production of LLZO in the form of aglass-ceramic. A glass-ceramic refers—as described above in the case ofthe phosphate-based solid-state lithium-ion conductors—to a materialwhich is produced by melt technology and converted subsequently into aglass-ceramic. The glass-ceramic contains an amorphous fraction of atleast 5 wt %. The amorphous fraction has a positive influence on theconductivity. However, the fraction of the amorphous phase ought not tobe greater than 40 wt %, preferably less than or equal to 30 wt %, sinceotherwise the overall conductivity is reduced. A further advantage ofproduction in the form of a glass-ceramic lies in the possibility ofexerting a direct influence over the microstructure through controlledcrystallization, thereby enabling further positive influencing of theconductivity. The glass-ceramic described in DE 102014116378 A1preferably has an ion conductivity of at least 5×10⁻⁵ S/cm, morepreferably at least 1×10⁻⁴ S/cm. In some cases the ion conductivity mayeven be considerably higher still.

SUMMARY

It is an object of the present invention to provide alithium-ion-conducting composite material comprising at least onepolymer and lithium-ion-conducting particles, where the compositematerial is to have a substantially higher particle fill level than hashitherto been achievable. The material is to be simpler and moreeconomical to produce. A further object of the invention is to find aprocess for producing a lithium-ion conductor from the compositematerial.

The object is achieved by means of a lithium-ion-conducting compositematerial, comprising at least one polymer and lithium-ion-containingparticles, where the particles have a sphericity Ψ of at least 0.7 andwhere the composite material comprises at least 20 vol % of theparticles for a polydispersity index PI of the particle sizedistribution of <0.7, or where the composite material comprises at least30 vol % of the particles for a polydispersity index PI of the particlesize distribution in the range from 0.7 to <1.2, or where the compositematerial comprises at least 40 vol % of the particles for apolydispersity index PI of the particle size distribution of >1.2.

The sphericity Ψ here is a parameter of how sphere-shaped the particleis.

According to the definition of H. Wadell, the sphericity Ψ of a particleis calculated as the ratio of the surface area of a sphere of equalvolume to the surface area of the particle:

$\Psi = \frac{\sqrt[3]{36\;\pi\; V_{p}^{2}}}{A_{p}}$

where V_(p) denotes the volume of the particle and A_(p) its surfacearea.

Typical sphericity values Ψ for different types of particle are asfollows:

Sphere: 1.0

Drop, bubble, round grain: 0.7-1.0

Angular grain: 0.45-0.6

Needle-shaped particle: 0.2-0.45

Platelet-shaped particle: 0.06-0.16

Particle with severely riven surface: 10⁻⁸-10⁻⁴

High sphericities Ψ in the sense of the present invention are achievedwhen Ψ has a value of at least 0.7.

By the polydispersity index, PI, of the particle size distribution ismeant, in the sense of the invention, the base-ten logarithm of thequotient formed from the d₉₀ and the d₁₀ values of the distribution:PI=log(d ₉₀ /d ₁₀)

Generally speaking, higher particle fill levels can be achieved incomposites and composite precursors for broader particle sizedistributions, in other words if the polydispersity index PI adoptslarger values.

Definition of d, Especially d₉₀ Values and d₁₀, for Determining PI:

Independently of their sphericity Ψ, the particles of a powder aregenerally distinguished with the aid of a volume-equivalent spherediameter, which has to be measured, and are ordered into selectedclasses according to their size. To represent a particle sizedistribution, a determination is made of the quantity fractions withwhich the respective classes of particle are present in the powder.

This is done using different quantity types. If the particles arecounted, the quantity type is the number. In the case of weighings,conversely, it is the mass or, in the case of homogeneous density

, the volume. Other types are derived from lengths, projection surfacesand surface areas.

The following are distinguished:

Quantity type: Index r: Number 0 Length 1 Area 2 Volume (mass) 3

One common quantity measure for describing the particle sizedistribution in powders is formed by the cumulative distribution

. The index r identifies the quantity type according to the table above.

The cumulative distribution function Q_(r)(d) indicates the standardizedquantity of all particles having an equivalent diameter less than orequal to d. Explicitly defined below are cumulative distributions of thetwo most commonplace quantity types:

Particle Number (r=0)

Let N_(i) be the number of all particles investigated with a diameter dless than or equal to the diameter d_(i) under consideration and let Nbe the total number of all particles investigated. In that case

${Q_{0}\left( d_{i} \right)} = \frac{N_{i}}{N}$Particle Mass (r=3)

Let m_(i) be the mass of all particles investigated with a diameter dless than or equal to the diameter d_(i) under consideration, and let mbe the total mass of all particles investigated. In that case

${Q_{3}\left( d_{i} \right)} = \frac{m_{i}}{m}$

In the sense of the invention, d_(i) values are understood to beequivalent diameter values for which the Q₃(d_(i)) cumulativedistribution function adopts the following values:

-   -   d₁₀: Q₃(d₁₀)=10%, i.e. 10 wt % of the particles have a diameter        less than or equal to d₁₀.    -   d₅₀: Q₃(d₅₀)=50%, i.e. 50 wt % of the particles have a diameter        less than or equal to d₅₀.    -   d₉₀: Q₃(d₉₀)=90%, i.e. 90 wt % of the particles have a diameter        less than or equal to d₉₀.    -   d₉₉: Q₃(d₉₉)=99%, i.e. 99 wt % of the particles have a diameter        less than or equal to d₉₉.    -   d₁₀₀: Q₃(d₁₀₀)=100%, i.e. 100 wt % of the particles have a        diameter less than or equal to d₁₀₀.

In the sense of the present specification, the term “polydispersityindex” may be understood synonymously with the term “polydispersionindex”.

The composite material of the invention may be used a) in one embodimentdirectly as a lithium-ion conductor or b) in another embodiment as anintermediate for further processing to give a lithium-ion conductor.

Surprisingly it has emerged that with particles having a sphericity Ψ ofat least 0.7 it is possible to achieve a substantially higher particlefill level. Accordingly, composite materials of the invention areaccessible which comprise at least 20 vol % of the particles when thepolydispersity index PI of the particle size distribution has a value of<0.7, or which comprise at least 30 vol % of the particles when thepolydispersity index PI of the particle size distribution has a value of0.7≤PI<1.2, or which comprise at least 40 vol % of the particles whenthe polydispersity index PI has a value of ≥1.2.

In one particularly preferred embodiment of the invention, the particleshave a sphericity Ψ of at least 0.8 and more preferably of at least 0.9.

In a further embodiment, the composite material preferably comprises atleast 25 vol % of the particles and more preferably at least 30 vol % ofthe particles if the polydispersity index PI of the particle sizedistribution has a value of <0.7, preferably at least 35 vol % of theparticles and more preferably at least 40 vol % of the particles if thepolydispersity index PI of the particle size distribution has a value of0.7≤PI<1.2, or preferably at least 45 vol % of the particles and morepreferably at least 50 vol % of the particles if the polydispersityindex PI of the particle size distribution has a value of ≥1.2.

The polymer preferably comprises at least one of the followingcompounds: polyethylene oxide, derivatives of polyethylene oxide,polyvinyl butyral.

Furthermore, the use of the following polymers is conceivable:polyacrylonitrile, polyester, polypropylene oxide, ethyleneoxide/propylene oxide copolymer, polyethylene oxide crosslinked withtrifunctional urethane, poly(bis(methoxy-ethoxy-ethoxide))phosphazene(MEEP), triol-like polyethylene oxide crosslinked with difunctionalurethane, poly((oligo)oxethylene) methacrylate-co-alkali metalmethacrylate, polymethyl methacrylate (PMMA), polymethylacrylonitrile(PMAN), polysiloxanes and also their copolymers and derivatives,polyvinylidene fluoride or polyvinylidene chloride and also thecopolymers and derivatives thereof, poly(chlorotrifluoroethylene),poly(ethylene-chlorotrifluoroethylene), poly(fluorinatedethylene-propylene), acrylate-based polymers, condensed or crosslinkedcombinations thereof, and/or physical mixtures of these.

The polymer can comprise at least one lithium-ion-conducting compound,more particularly lithium bistrifluoromethanesulfonimidate aslithium-ion-conducting compound.

Further suitable conductive salts that can be used include thefollowing. LiAsF₆, LiClO₄, LiSbF₆, LiPtCl₆, LiAlC₄, LiGaCl₄, LiSCN,LiAlO₄, LiCF₃CF₂SO₃, Li(CF₃)SO₃ (LiTf), LiC(SO₂CF₃)₃, phosphate-basedlithium salts, preferably LiPF₆, LiPF₃(CF₃)₃(LiFAP) and LiPF₄(C₂O₄)(LiTFOB), borate-based lithium salts, preferably LiBF₄, LiB(C₂O₄)₂(LiBOB), LiBF₂(C₂O₄) (LiDFOB), LiB(C₂O₄)(C₃O₄) (LiMOB), Li(C₂F₅BF₅)(LiFAB) and Li₂B₁₂F₁₂ (LiDFB) and/or lithium salts of sulfonylimides,preferably LiN(FSO₂)₂ (LFSI), LiN(SO₂CF₃)₂ (LiTFSI) and/or LiN(SO₂C₂F₅)₂(LiBETI).

Besides the stated polymer electrolyte it is also possible,alternatively, for a polyelectrolyte to be employed. These are polymers,an example being polystyrenesulfonate (PSS), which carries Li⁺ ascounter-ion, or polymerized imidazolium-, pyridinium-, phosphonium- orguanidinium-based ionic liquids which carry a discrete number ofchemically bonded ionic groups and for that reason are intrinsicallylithium-ion-conductive.

The lithium-ion-conducting particles consist preferably of at least onelithium-ion-conducting compound, more particularly of at least thefollowing lithium-ion-conducting compounds: lithium lanthanum zirconate(LLZO), lithium aluminium titanium phosphate (LATP) compounds withgarnet-like crystal structure, composed more particularly of a materialwith a garnet-like crystal structure having the empirical formulaLi_(7+x−y) M_(x) ^(II) M_(3−x) ^(III) M_(2−y) ^(IV) M_(y) ^(V) O₁₂where: M^(II) is a divalent cation, M^(III) is a trivalent cation,M^(IV) is a tetravalent cation, and M^(V) is a pentavalent cation, wherepreferably 0≤x<3, more preferably 0≤x≤2, 0≤y<2, and very preferably0≤y≤1 or compounds derived therefrom, are more particularly of compoundsdoped with Al, Nb or Ta, compounds having a crystal structureisostructural with NaSICon, more particularly having the empiricalformula Li_(1+x−y)M⁵⁺ _(y)M³⁺ _(x)M⁴⁺ _(2−x−y)(PO₄)₃, where x and y arein the range from 0 to 1 and (1+x−y)>1 and M is a cation of valency +3,+4 or +5, or compounds derived therefrom.

The particles preferably have an average particle diameter in the rangefrom 0.02 μm to 100 μm, more preferably in the two ranges 0.2 μm to 2 μmand 5 μm to 70 μm, and more preferably in one of the two ranges 0.2 μmto 2 μm or 5 μm to 70 μm.

In a further preferred embodiment, for the lithium-ion-conductingcomposite material, the interfacial resistance for the lithium-ionconductivity between the polymer and the particles is reduced as aresult of a surface modification of the particles and therefore thelithium-ion conductivity is greater than for a comparable compositematerial wherein the interfacial resistance between the polymer and theparticles is not reduced.

The particles have preferably been produced by means of at least one ofthe following processes: spray calcination (especially using thepulsation reactor technology), filamentization from a salt melt, dropletformation, and glass sphere production.

Irrespective of the issue whether the purely inorganic solid-statelithium-ion conductors are oxide-based, phosphate-based orsulfide-based, a feature common to all of the methods described to datein the prior art for producing them is that the lithium-ion-conductingmaterial obtained in the process in question is obtained eithermonolithically or else at least in indefinitely coarse-grainedstructure, and must be brought into a final presentation form, as apowder with defined particle size and particle size distribution, bymeans of further size-reduction steps, generally fine grindingprocesses. The target particle size is frequently in the μm or sub-μmrange. Only by this means is further processing possible. Particularforms of processing here include on the one hand incorporation into apolymer, polymer electrolyte or polyelectrolyte for the final productionof a hybrid electrolyte. Alternatively, the operation in question may becompression moulding or may be that of incorporation into a ceramic slipand further processing thereof in a shaping step (e.g. tape casting) toform a green ceramic body which by sintering is converted into a ceramiccomponent ultimately consisting purely of the inorganic solid-state ionconductor.

Comminuting processes, such as said fine grinding processes, forexample, make the production of spherical powder particles virtuallyimpossible. Instead, they produce fragmentary particles, featuring edgesand angles. These particles, accordingly, have a sphericity ofsignificantly less than 0.7.

In many applications, non-spherical particles of a single material aremuch more difficult to process than their spherical pendants, assumingthe same particle size and particle-size distribution. This circumstanceis manifested in particular on incorporation into thermoplastic matrices(as in the case of production of hybrid electrolytes for example) andinto liquid matrices (relevant, for example, in the case of theproduction of ceramic slips). For the same volume fill levels, theviscosity of the particle-filled formulation is significantly higher inthe case where non-spherical particles are used than for the use ofspherical particles of the same material, provided the latter possess acomparative particle size and/or particle-size distribution.

Conversely, in the case of the spherical variant, such formulations canbe provided with significantly higher fill levels than in the case ofthe non-spherical embodiment. The reason for this is that the internalfriction in formulations filled with non-spherical particles isincreased by the tendency of the particles to get caught up with oneanother when they move past one another within the formulation as aresult of the action of external shearing forces. In the case ofspherical particles, in contrast, they are better able to slide past oneanother.

The capacity to achieve much higher volume fill levels under comparableconditions when using spherical particles in formulations filledtherewith is of great relevance in practice: in hybrid electrolytes, forexample, as a result of increased incorporation of the solid-stateinorganic ion conductor, consisting of spherical particles, it ispossible to achieve much better lithium-ion conductivities, because thelithium-ion conductivity of the inorganic constituent is generallyhigher than that of the polymer-based matrix. Even at relatively highfill levels, ceramic slips remain pourable if spherical particles areemployed in their formulation. The green body resulting after drying ofthe solvent subsequently has a much lower porosity, leading tosignificantly less contraction in the final sintering step. Artefactsfrequently associated with contraction during sintering (such ascracking, for example, etc.) can be reduced significantly in theireffect in this way.

In view of the prior art, therefore, the desire is for pulverulent,lithium-ion-conducting, solid electrolyte materials which consist ofmicroscale or sub-microscale particles having a high sphericity Ψ.

By way of example, the following processes will be recited:

GLASS SPHERE PRODUCTION: the path to producing particles fromlithium-ion-conducting material makes use of the fact that one of theways in which these materials can be produced is via the glass-ceramicroute: for this purpose, in a commonplace melting process, a greenglass—which ideally is crystal-free—is first melted, and in the courseof a downstream heating step is ceramicized and at the same timeconverted into the actual glass-ceramic. During cooling, the glass meltproduced in the first process step may in principle be subjected to thecustomary hot shaping processes employed for the production of glassspheres. For this purpose, the following process approaches areconceivable: in the process disclosed in U.S. Pat. No. 3,499,745, amolten glass jet is caused to impinge on a striking wheel which, whensufficiently high forces are realized, causes the glass jet to break upinto component strands, referred to as filaments. These filaments aresubsequently spun first through a heated region, a cooling region, andfinally into a collection zone. Because of the tendency to minimize thesurface tension, this tendency taking effect after the formation offilaments, the filaments become round. According to EP 1 135 343 B1, asufficient sphericity is achieved when the relaxation time T elapsingfrom the time of filament formation can be described by the equationT=(d×μ)/6. In this equation, d is the diameter of the spheres formed, Lis the viscosity of the filament and 6 is the surface tension of thefilament during the relaxation time. As described in U.S. Pat. No.3,495,961, the striking wheel may also be replaced by a rotor. Otherknown processes for producing the glass spheres include the inflation ofa burning gas stream through a molten glass stream in order to divide upthe glass into individual particles. Such processes are disclosed inU.S. Pat. No. 3,279,905. For this purpose, alternatively, glassparticles of relatively low sphericity may be (partially) melted again,as described in DD 282 675 A5, by being introduced into a flame,whereupon they undergo rounding.

FILAMENTIZATION OF SALT MELTS: In analogy to the filament formationdescribed above and to the subsequent formation of spherical drops froma molten glass jet, owing to relaxation effects for reducing the surfaceenergy, this process may take place correspondingly from a jet ofmaterial generated from a salt melt. In technological terms, it ispossible here to proceed similarly, bearing in mind that the viscosityof a molten glass may differ considerably from that of a salt melt,according to the temperature selected in the respective case. Thematerial in droplet form must be converted first of all—by passagethrough an even hotter region—into a pre-ceramic intermediate, which isfrequently porous but, apart from isotropic contraction, isdimensionally stable—and must subsequently be converted further—eitherstill in the same heating step or in a separate, additional, downstreamheating step—into the actual solid-state lithium-ion conductor. In thisway, ideally, densely sintered spheres of the solid-state lithium-ionconductor material are obtained.

SPRAY CALCINATION (USING THE PULSATION REACTOR TECHNOLOGY): When using apulsation reactor, as disclosed in DE 10111938 A1, DE 102006027133 A1,DE 102006039462 A1 or EP 1927394 A1, a gaseous or a liquid mixture inthe form of a solution, suspension or dispersion comprising all thecomponents for producing the lithium-ion-conducting material isintroduced into a pulsating stream of hot gas—in the latter case, byfine atomization. The pulsating stream of hot gas itself is generatedwithin a hot gas generator in the reactor, through the combustion ofnatural gas or hydrogen with ambient air. Depending on the positionchosen for sprayed introduction, the temperatures prevailing there arebetween 500 and 1500° C. Within the pulsating stream of hot gas, anintermediate is formed which, by further thermal aftertreatment in thesame reactor or in a different reactor, is converted into the ultimateform. In the former case, the reactor may be provided with an additionalfuel supply, which is positioned downstream of the point of sprayintroduction, along the pulsating stream of hot gas.

DROPLET FORMATION PROCESS: In the case of the droplet formation process,the starting point is an aqueous or solvent-based salt solution or a solas precursor for the lithium-ion-conducting material, or else ananoparticulate solution of the lithium-ion-conducting material, and thesol or solution is converted into droplets via a suitable nozzleapparatus. After they have been formed, the droplets either are drieddirectly in a suitable process gas stream, as described in U.S. Pat. No.4,043,507 or 5,500,162, or else first, by introduction into a suitableliquid medium, as disclosed in U.S. Pat. Nos. 5,484,559, 6,197,073, US2004/0007789 A1 or WO 2015/014930 A1, are first stimulated to furtherflocculation and subsequently are aged, washed and dried. The spherical,porous green bodies produced in this way undergo a subsequent sinteringstep in which they are compacted to form a lithium-ion-conductingceramic body with high sphericity.

The object is achieved, moreover, by a process for producing alithium-ion conductor, in which the composite material of the inventionis sintered, more particularly under the action of elevated temperatureand/or elevated pressure.

DETAILED DESCRIPTION

According to requirements and field of use, both thelithium-ion-conducting composite material of the invention and alithium-ion conductor produced from the lithium-ion-conducting compositematerial may be used as a lithium-ion-conducting component orconstituent of such a component.

Further described are formulations for producing composite precursorsfor hybrid electrolytes or ceramic slips for producing sintered, purelyinorganic, solid-state lithium-ion conductor components, in which, atthe same volume fill levels, the viscosity of the particle-filledformulation when using non-spherical particles is significantly higherthan when using the particles of high sphericity Ψ used in accordancewith the invention, provided that particle size and/or particle-sizedistribution are the same in both cases.

Moreover, formulations for producing composite precursors for hybridelectrolytes or ceramic slips for producing sintered, purely inorganic,solid-state lithium-ion conductor components are described in which thecorresponding formulations, without substantial change in the viscosity,can be provided with significantly higher fill levels in the case of thespherical variant than in the case of the non-spherical embodiment. Theproviso in this case again is that in both cases there are nosubstantial differences in particle size and particle-size distribution.

The lithium-ion-conducting material produced in accordance with theinvention in the form of spherical particles with size in the μm- orsub-μm range may be incorporated as filler into a polymer electrolyte orinto polyelectrolytes, in which case the resulting composite ispopularly referred to as a hybrid electrolyte. Alternatively to this, itmay be compressed to a compact using suitable tooling, or incorporatedinto a ceramic slip (with or without the addition of a binder), andsubjected to a suitable shaping process (e.g. tape casting), and in bothcases may be sintered at temperature to form a purely inorganic,ion-conducting moulding. Both forms of presentation—hybrid electrolyteand purely inorganic, ceramic, solid-state ion conductor—may be used assolid-state electrolytes in next-generation rechargeable lithium orlithium-ion batteries, as for example in solid-state lithium batteries(all-solid-state batteries (ASSB)) or lithium-air batteries. Onepossibility is the use thereof as a separator introduced between theelectrodes, it preserves them from unwanted short-circuiting and soensures the functional capacity of the system as a whole. For thispurpose, the corresponding composite may either be applied as a layer toone or both electrodes or integrated as a self-standing membrane, in theform of a solid-state electrolyte, into the battery. An alternativepossibility is that of compounding with the active electrodematerials—in the case of the hybrid electrolyte, by incorporation on theactive electrode material into the hybrid electrolyte formulation; inthe case of the purely inorganically ceramic electrolyte, byco-sintering with that electrolyte. In this case, the solid-stateelectrolyte brings about the transport of the relevant charge carriers(lithium ions and electrons) to the electrode materials and to or awayfrom the conducting electrodes, according to whether the battery isbeing discharged or charged.

WORKING EXAMPLES

Examples of production of lithium-ion-conducting particles of highsphericity Ψ of at least 0.7 from a lithium-ion-conducting material:

Production of Spherical LAGP Particles

Shaping Directly from the Green Glass Melt

A starting glass for an eventually lithium-ion-conducting,phosphate-based glass-ceramic of the composition 5.7 wt % Li₂O, 6.1 wt %Al₂O₃, 37.4 wt % GeO₂ and 50.8 wt % P₂O₅ was melted in a dischargecrucible at a temperature of 1650° C.

In the melting assembly selected, the glass melt was held at atemperature of 1600° C. It was discharged from a nozzle with a diameterof 2 mm, positioned on the base of the crucible. The glass jet thusproduced was dropped onto a 53-toothed striking wheel 8 mm thick andwith an outer diameter of 135 mm, this wheel rotating at a frequency of5000 rpm about its own axis. In this way, the glass stream wasfilamentized into individual sub-strands, and accelerated with an angleof inclination of between 20 to 300 as measured with respect to thehorizontal. It was subsequently passed through a tubular furnace 3 mlong, constructed in a curved shape and heated to 1550° C. with two gasburners, this furnace mimicking the flight path of the filamentizedglass stream. As a result of the tendency to minimize the surfaceenergy, the filaments in elongate form underwent a change in shape tospheres. Following emergence from the tubular furnace, the glass sphereswere cooled by further flight in air until sufficient dimensionalstability was achieved, and were finally captured in a collectingvessel.

The cooled, very largely X-ray-amorphous green glass spheres produced bythe hot shaping process described were ceramicized and so converted intothe eventual, lithium-ion-conducting glass-ceramic in the course of afurther temperature treatment after nucleation in the temperature rangebetween 500 and 600° C. for 2 to 4 hours with a maximum temperature of850° C. and a hold time of 12 hours.

Shaping by Rounding of Non-Spherical Green Glass Particles

A starting glass for an eventually lithium-ion-conducting,phosphate-based glass-ceramic of the composition 5.7 wt % Li₂O, 6.1 wt %Al₂O₃, 37.4 wt % GeO₂ and 50.8 wt % P₂O₅ was melted in a dischargecrucible at a temperature of 1650° C.

In the melting assembly selected, the glass melt was held at atemperature of 1600° C. It was discharged from a nozzle with a diameterof 2 mm, positioned on the base of the crucible into a nip between twocontra-rotating, water-cooled rolls, where it was quenched to form agreen glass ribbon. The green glass ribbon was singularized into smallsplinters mechanically, using a hammer.

The glass splinters were roughly comminuted by preliminary grinding in abead mill, and the powder fraction having a particle size d₁₀₀<100 μmwas removed by sieving from this roughly comminuted material. This greenglass powder isolated by sieving was comminuted further in an additionaldownstream step of dry grinding in an opposed-jet mill to a particlesize with a distribution of d₁₀=0.9 μm, d₅₀=5 μm, d₉₀=13 μm and d₉₉=18μm.

By introduction of the powder into an oxyhydrogen gas flame, the glassparticles are melted again, and experience rounding in the process,owing to the tendency for minimization of the surface energy. Onemergence from the flame, the particles are allowed to cool and arecaptured in a collecting vessel.

The cooled, very largely X-ray-amorphous green glass spheres produced bythe hot shaping process described were ceramicized and so converted intothe eventual, lithium-ion-conducting glass-ceramic in the course of afurther temperature treatment after nucleation in the temperature rangebetween 500 and 600° C. for 2 to 4 hours with a maximum temperature of850° C. and a hold time of 12 hours.

Filamentization of Salt Melts

In a first step, a zirconium-containing precursor powder was produced asfollows: 23.4 kg (50.0 mol) of zirconium n-propoxide (70% solution) areadmixed dropwise with 5.0 kg (50.0 mol) of acetylacetone with stirringin a round-bottomed flask. The resulting reaction mixture is stirred atroom temperature for 60 minutes. Then 2.7 kg (150.0 mol) of distilledwater were added for hydrolysis. After a reaction time of about 1 hour,the resulting prehydrolysate was dried completely on a rotaryevaporator. A sample of the resultant powder is then heated to determinethe oxide content (900° C./5 hours).

1.77 kg (5.0 mol) ZrO₂ equivalent of the zirconium-containing precursorpowder (oxide content: 35 wt %) produced in the preceding step wereintroduced together with 2.5 kg (7.5 mol) of lanthanum acetatesesquihydrate, 1.95 kg (19.2 mol) of lithium acetate dihydrate and 0.15kg (0.61 mol) of aluminium chloride hexahydrate into a ball mill, wherethey were ground for 4 hours to produce an ideally homogeneous powdermixture. The grinding balls used for this purpose were Al₂O₃ balls witha diameter of 40 mm.

After sieving to remove the balls, the powder mixture was placed into anAl₂O₃ discharge crucible where it was brought to a temperature of 300°C., just above the melting point of anhydrous lithium acetate, which is280-285° C. A salt melt is formed which was discharged via a nozzle witha diameter of 2 mm that was positioned on the base of the crucible. Thejet generated in this way and consisting of the salt melt was droppedonto a 53-toothed striking wheel 8 mm thick with an outer diameter of135 mm, this wheel rotating at a frequency of 5000 rpm about its ownaxis. In this way, the jet consisting of the salt melt was filamentizedinto individual strands and accelerated with an angle of inclination ofbetween 20 to 300 as measured with respect to the horizontal. It wassubsequently passed through a tubular furnace 3 m long and of curvedconstruction that mimicked the flight path of the filamentized jetconsisting of the salt melt. The furnace was heated electrically so asto be maintained in the entry zone at moderate temperatures of 300-320°C., so that the salt melt was retained and the filaments, initiallystill of elongate form, underwent a change in shape, owing to thetendency for minimization of the surface energy, into spheres which arestill liquid. In the downstream zones, the temperature selected was thensignificantly higher—temperatures of around 900° C. were achieved here.Here, therefore, there was a first step of calcination of the liquidspheres, forming porous, preceramic particles as an intermediate.Following emergence from the tubular furnace, these spheres were allowedto cool by further flight in air and were finally captured in acollecting vessel.

The porous, preceramic particles were compacted in a further calcinationstep in an oven at 1050° C. with a hold time of 7-8 hours to give thefinal spheres consisting of the lithium-ion-conducting LLZO material.

Production of Spherical LLZO Particles Via Spray Calcination Using thePulsation Reactor Method

2.3 kg (4.7 mol) of zirconium acetylacetonate were dissolved in at least10.0 kg (556 mol) of distilled water in a suitable reaction vessel. 2.4kg (7 mol) of lanthanum acetate sesquihydrate were dissolved in afurther reaction vessel in 10 kg (556 mol) of distilled water. 1.8 kg(18 mol) of lithium acetate dihydrate and 0.14 kg (0.58 mol) ofaluminium chloride hexahydrate were dissolved in a third reaction vesselin 5.0 kg (278 mol) of distilled water. After complete dissolution ofthe components, the solutions were combined and the resulting reactionmixture was stirred at room temperature for 12 hours.

The solution is conveyed with the aid of a peristaltic pump into apulsation reactor at a volume flow rate of 3 kg/h, where via a 1.8 mmtitanium nozzle it is finely atomized into the reactor interior, whereit is subjected to thermal treatment. The temperature of the combustionchamber here is maintained at 1030° C., and that of the resonance tubeat 1136° C. The ratio of the quantity of combustion air to the quantityof fuel (natural gas) is 10:1 (airgas).

The powder is introduced into a cuboidal alpha-alumina crucible andplaced in a chamber kiln. The material for calcining is brought to atemperature of 1050° C. in the kiln, in an air atmosphere, for thecomplete compaction of the spherical microscale particles consisting ofthe LLZO.

Production of Spherical LLZO Particles Via the Droplet Formation Process

The LLZO material was first of all melted in a so-called skull crucible,as described in DE 199 39 782 C1, for instance. Employed for thispurpose was a water-cooled crucible in which, during melting, a coolerprotective layer of the material to be melted is formed. Accordingly, nocrucible material is dissolved during the melting operation. The inputof energy into the melt is accomplished by means of radio-frequencycoupling via the surrounding induction coil into the molten material. Acondition here is the sufficient conductivity of the melt, which in thecase of lithium garnet melts is assured by the high lithium content.During the melting process, evaporation of lithium occurs, and caneasily be corrected by an excess of lithium. For this purpose it isnormal to operate with a 1.1- to 2-fold lithium excess.

The raw materials were mixed in accordance with the followingcomposition and introduced into the skull crucible, which is open at thetop: 14.65 wt % Li₂O, 56.37 wt % La₂O₃, 21.32 wt % ZrO₂ and 7.66 wt %Nb₂O₅. It was necessary first of all to preheat the batch in order toachieve a certain minimum conductivity. This was done using a burnerheating system. When the coupling temperature was reached, furtherheating and homogenization of the melt were achieved via radio-frequencycoupling via the induction coil. In order to improve the homogenizationof the melts, stirring took place with a water-cooled stirrer.

The material produced in this way may in principle be converted, eitherby direct solidification from the melt or by quenching, followed by atemperature treatment (ceramicization) into a glass-ceramic materialwith a garnet-like main crystal phase. In the example described here,the variant selected was that of direct quenching.

In this case, the material was obtained as a monolithic block, which wasconverted into a powder having a particle size d₁₀₀<100 μm via a varietyof rough comminution processes—such as processing with hammer and chiselin the first step, comminution of the fragments obtainable in that case,using a jaw crusher in the second step, and further preliminary grindingof the resultant coarse powder in the planetary mill, with subsequentsieving, in the third step. In a further downstream step, this powderwas comminuted further by grinding in water, this being carried out inan attritor, to a particle size having a distribution of d₁₀=0.14 μm,d₅₀=0.42 μm, d₉₀=1.87 μm and d₉₉=2.92 μm. The content of LLZO solids inthe grinding slip used in this case was around 30%. To stabilize theparticles, a dispersant (Dolapix CE 64 or Dolapix A88 from Zschimmer &Schwarz GmbH & Co. KG) was added to the slip prior to grinding, with afraction of 1.0%, based on the LLZO fraction in the suspension, provingto be highly practicable.

For further processing, the solids content of the grinding slip wasincreased to a level of 60% by partial evaporation of the water on therotary evaporator, to obtain a suitable mixing ratio in respect of theviscosity.

Then ammonium alginate was added as a binder in an amount of 1.0%.

By means of a droplet formation process involving nozzles and/or hollowneedles, dimensionally stable green bodies with sizes of 0.3 to 2.5 mmwere obtained from the slip by immersion and also reaction in analuminium lactate solution or an inorganic acid solution or an organicacid solution.

These green bodies were subsequently shaped to form sintered beads by asintering process. Sintering took place in an air atmosphere understandard pressure at temperatures of 1150° C.

Examples for the production of formulations of lithium-ion-conductingcomposite materials filled with at least 20 vol % oflithium-ion-conducting particles with high sphericity Ψ of at least 0.7from a lithium-ion-conducting material with a polydispersity index PI ofthe particle size distribution of <0.7, or at least 30 vol % ofcorresponding particles at a polydispersity index PI of the particlesize distribution of 0.7<PI<1.2, or at least 40 vol % of correspondingparticles at a polydispersity index PI of the particle size distributionof >1.2.

Production of a composite material of the invention (production of ahybrid electrolyte membrane based on a polyethylene oxide (PEO) filledwith LLZO particles/lithium bis(trifluoromethanesulfonyl)imide (LiTSFI)polymer electrolyte).

1.4 g of polyethylene oxide (PEO, Dow Chemical) having a molar weight of4×10⁶ g/mol were dried under reduced pressure at 50° C. for 48 hours.Added to the polymer under dry room conditions (dew point <−70° C.) were8.5 g of lithium lanthanum zirconium oxide powder, consisting ofparticles having a sphericity of 0.92 and a particle size distributionas follows: d₁₀=1.22 μm, d₅₀=2.77 μm, d₉₀=5.85 μm d₉₉=9.01 μm.Correspondingly, in accordance with the invention, the polydispersityindex PI of the particle size distribution is 0.681. The mixture wassubjected to intensive grinding in a mortar. It was then admixed with0.6 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 3M) havinga purity of >99% (suitable for battery applications), which had beendried beforehand under reduced pressure (10⁻⁷ bar) at 120° C. for 24hours. All of the components were further mixed intensely in the mortar,to form, finally, a homogeneous paste. This resulted in a PEO/LiTSFIpolymer electrolyte matrix having a ratio of lithium ions to ethyleneoxide monomer units (Li:EO) of 1:15, in which the inorganic solid-statelithium-ion conductor was embedded in a volume fraction of 50 vol %. Thehybrid electrolyte thus produced was vacuum-welded into a pouch,heat-treated overnight at 100° C. and then subjected to hot pressing at100° C. with an applied force of 50 kN (50-750 kg/cm²) (ServitecPolystat 200 T press). This gave a composite membrane having a thicknessof around 100 μm.

The same procedure was used to produce hybrid electrolyte membranes,using an LLZO powder consisting of non-spherical particles (Ψ=0.48), theparticle size distribution being as follows: d₁₀=0.44 μm, d₅₀=1.24 μm,d₉₀=3.50 μm, d₉₉=6.94 μm. The polydispersity index of the particle sizedistribution, PI, was in this case, in accordance with the invention,0.900. In these cases, however, only 4.6 g of LLZO powder could beincorporated practicably into the pEO/LiTSFI polymer electrolyte matrix;in these cases, in other words, the hybrid electrolyte was producibleonly with a maximum volume content of 29 vol %.

Production of a lithium-ion conductor of the invention from thecomposite material of the invention (production of a purely inorganic,sintered solid-state electrolyte membrane by means of a tapecastingprocess, based on a casting slip filled with LATP particles)

11.4 g of polyvinyl butyral (PVB) having a molar weight of 35 000 g/mol,containing the vinyl butyral units and also 1.7 wt % of vinyl acetateand 18.9 wt % of vinyl alcohol units, were dissolved in 68.4 g of asolvent mixture consisting of ethanol and toluene (4:6). The viscosityof the solution was between 200 and 450 mPa s. The mixture was admixedwith 5.7 g of dioctyl phthalate, which functioned as a plasticizer.Introduced finally into the mixture by dispersion, using a dissolver,were 200 g of a lithium aluminium titanium phosphate (LATP)glass-ceramic powder, which consisted of particles having a sphericityof 0.94 and a particle size distribution as follows: d₁₀=0.81 μm,d₅₀=2.23 μm, d₉₀=5.17 μm, d₉₉=8.46 μm. In accordance with the invention,the polydispersity index PI of the particle size distribution in thiscase was 0.805. The resulting casting compound had a viscosity of4000-5000 mPa s. The glass-ceramic powder content was around 43 vol %.

The homogenized compound produced in this way was subsequently freedfrom gas bubbles (i.e. deaerated) by means of vacuum technology. Thisdeaerated material was supplied to the customary tapecasting process ona film-drawing apparatus, and in that way was cast into a tape with athickness (measured after drying) of around 0.3 mm. The green tapeproduced in this way was thereafter cut to the desired format and sosingularized.

The singularized tape sections were finally sintered at 1000° C. for 4hours to form dense LATP membranes. Tape shrinkage in this process wasaround 9%.

In accordance with the same procedure, a purely inorganic solid-statelithium-ion conductor membrane was produced, using an LATP powder whichconsisted of non-spherical particles (Ψ=0.46) and had a particle sizedistribution as follows: d₁₀=0.68 μm, d₅₀=1.74 μm, d₉₀=3.86 μm, d₉₉=7.21μm. The polydispersity index of the particle size distribution, PI, wasin this case 0.754, in accordance with the invention. In these cases,however, it was possible for only 90 g of LATP powder to be incorporatedpracticably into the binder solution consisting of PVB, dioctylphthalate and ethanol/toluene, meaning that in these cases thetapecasting slip could only be produced with a volume content of max. 28vol % without significantly exceeding the target viscosity of 4000-5000mPa s. On account of the significantly reduced solids content, thecontraction during sintering was around 15%.

What is claimed is:
 1. A lithium-ion-conducting composite material, comprising: a polymer selected from the group consisting of polyethylene oxide, derivatives of polyethylene oxide, polyvinyl butyral, and combinations thereof; and lithium-ion-conducting particles having a sphericity Ψ of at least 0.7, wherein the lithium-ion-conducting particles comprise a lithium-ion-conducting compound selected from the group consisting of lithium lanthanum zirconate (LLZO), lithium aluminum titanium phosphate (LATP), and combinations thereof, wherein the lithium-ion-conducting particles have a polydispersity index of at least 0.7 and are present in at least 30 vol % of the composite material, and wherein the lithium-ion-conducting particles have an average particle diameter of 0.02 μm to 100 μm.
 2. The lithium-ion-conducting composite material of claim 1, wherein the lithium-ion-conducting particles have an average particle diameter of 0.2 μm to 2 μm.
 3. The lithium-ion-conducting composite material of claim 1, wherein the lithium-ion-conducting particles have an average particle diameter of 5 μm to 70 μm.
 4. The lithium-ion-conducting composite material of claim 1, wherein the lithium-ion-conducting particles are spray calcination particles.
 5. The lithium-ion-conducting composite material of claim 4, wherein the lithium-ion-conducting particles are pulsation reactor particles.
 6. A lithium-ion-conducting composite material, comprising: a polymer selected from the group consisting of polyethylene oxide, derivatives of polyethylene oxide, polyvinyl butyral, and combinations thereof; and lithium-ion-conducting particles having a sphericity Ψ of at least 0.9, wherein the lithium-ion-conducting particles comprise a lithium-ion-conducting compound selected from the group consisting of lithium lanthanum zirconate (LLZO), lithium aluminum titanium phosphate (LATP), and combinations thereof, and wherein the lithium-ion-conducting particles have a polydispersity index of >1.2 and are present in at least 40 vol % of the composite material, and wherein the lithium-ion-conducting particles have an average particle diameter of 0.02 μm to 100 μm.
 7. The lithium-ion-conducting composite material of claim 1, wherein the lithium-ion-conducting particles have a sphericity Ψ of at least 0.9.
 8. The lithium-ion-conducting composite material of claim 1, wherein the lithium-ion-conducting particles have a polydispersity index of >1.2 and are present in least 40 vol % of the composite material. 